Combination sensor

ABSTRACT

A fluid sensor including a sensing area configured to receive a fluid. The fluid sensor includes a transducer and a capacitive sensor. The transducer is configured to output an ultrasonic wave through the fluid. The capacitive sensor includes a capacitive plate configured to reflect the ultrasonic wave toward the transducer.

RELATED APPLICATIONS

This application claims priority to, and is a divisional patentapplication of, U.S. patent application Ser. No. 15/612,640, filed onJun. 2, 2017, the entire contents of which are incorporated herein byreference.

FIELD

Embodiments relate to sensing characteristics of a fluid.

SUMMARY

Various devices and systems, for example, an internal combustion engine,a braking system, and others, require fluids (for example, oil, fuel,diesel exhaust fluid, brake fluid, transmission fluid, washer fluid,refrigerant, etc.). Often, a system requirement is that these fluidsmeet certain quantities or characteristics, for example, level,temperature, speed-of-sound, concentration, density, and dielectricconstant. Often times, sensing various fluid characteristics requires aplurality of sensing elements or sensors (for example, a sensor to sensetemperature and a different sensor to sense concentration).

Thus, one embodiment provides a combination sensor with which multiplecharacteristics of a fluid may be measured. One example provides a fluidsensor including a sensing area configured to receive a fluid. The fluidsensor includes a transducer and a capacitive sensor. The transducer isconfigured to output an ultrasonic wave through the fluid. Thecapacitive sensor includes a capacitive plate configured to reflect theultrasonic wave toward the transducer.

Another embodiment provides a method of sensing a fluid, the methodincluding outputting, via a transducer, an ultrasonic wave through thefluid. The method further includes reflecting, via a capacitive sensorhaving a capacitive plate, the ultrasonic wave.

Other aspects of various embodiments will become apparent byconsideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side view of a sensing system according to someembodiments.

FIG. 2 illustrates a top view of the sensing system of FIG. 1 accordingto some embodiments.

FIG. 3 is an exploded view illustrating a capacitive plate and acapacitive substrate of the sensing system of FIG. 1 according to someembodiments.

FIG. 4 is an enlarged view illustrating the capacitive plate and housingof the sensing system of FIG. 1 according to some embodiments.

FIG. 5 is a circuit diagram modeling circuitry of the sensing system ofFIG. 1 according to some embodiments.

FIG. 6 is a block diagram illustrating a control system of the sensingsystem of FIG. 1 according to some embodiments.

FIG. 7 is a flow chart illustrating a process of the sensing system ofFIG. 1 according to some embodiments.

FIG. 8 is a flow chart illustrating a process of the sensing system ofFIG. 1 according to some embodiments.

FIG. 9 is a flow chart illustrating a process of the sensing system ofFIG. 1 according to some embodiments.

FIG. 10 is a flow chart illustrating a process of the sensing system ofFIG. 1 according to some embodiments.

FIG. 11 is a flow chart illustrating a process for providing the sensingsystem of FIG. 1 according to some embodiments.

DETAILED DESCRIPTION

Before any embodiments are explained in detail, it is to be understoodthat these embodiments are not limited in their application to thedetails of construction and the arrangement of components set forth inthe following description or illustrated in the following drawings.Other embodiments are possible and the embodiments described are capablebeing practiced or of being carried out in various ways.

The phrase “series-type configuration” as used herein refers to acircuit arrangement in which the described elements are arranged, ingeneral, in a sequential fashion such that the output of one element iscoupled to the input of another, though the same current may not passthrough each element. For example, in a “series-type configuration,”additional circuit elements may be connected in parallel with one ormore of the elements in the “series-type configuration.” Furthermore,additional circuit elements can be connected at nodes in the series-typeconfiguration such that branches in the circuit are present. Therefore,elements in a series-type configuration do not necessarily form a true“series circuit.”

Additionally, the phrase “parallel-type configuration” as used hereinrefers to a circuit arrangement in which the described elements arearranged, in general, in a manner such that one element is connected toanother element, such that the circuit forms a parallel branch of thecircuit arrangement. In such a configuration, the individual elements ofthe circuit may not have the same potential difference across themindividually. For example, in a parallel-type configuration of thecircuit, two circuit elements in parallel with one another may beconnected in series with one or more additional elements of the circuit.Therefore, a circuit in a “parallel-type configuration” can includeelements that do not necessarily individually form a true “parallelcircuit.”

FIGS. 1 and 2 illustrate a sensing system 100. In some embodiments, thesensing system 100 is placed within a tank holding a fluid to be sensed.In certain instances, the sensing system 100 is placed on a bottom ofthe tank. The sensing system 100 senses one or more characteristics ofthe fluid within the tank. The fluid may be, for example, oil, fuel,diesel exhaust fluid, brake fluid, transmission fluid, washer fluid,refrigerant, water (for example, distilled water), etc. The sensingsystem 100 includes a housing 105, a main substrate, or printed-circuitboard, 110, a level sensor 115, a temperature sensor 120, aspeed-of-sound sensor 125, and a capacitive sensor 130. The housing 105may be formed or otherwise constructed from a plastic or similarmaterial. As will be described below, the printed-circuit board includesor has mounted thereon control electronics.

The printed-circuit board (PCB) 110 is electrically and/orcommunicatively connected to the level sensor 115, the temperaturesensor 120, the speed-of-sound sensor 125, and the capacitive sensor130. In some embodiments, the PCB 110 includes, or is electricallycoupled to, a sensor control system 300 (FIG. 6), which, among otherthings, provides power to the plurality of sensors, analyzes data fromthe plurality of sensors, and outputs the analyzed data to othercomponents such as an external device (for example, a control system ofa vehicle).

The level sensor 115 senses a level of the fluid within the tank.Information regarding the level of the fluid along with informationregarding the volume of the container in which the fluid is stored maybe used to determine a quantity of the fluid. In the illustratedembodiment, the level sensor 115 includes a level transducer 135 and alevel focus tube 140. The level transducer 135 acts as both atransmitter and receiver. In some embodiments, the level transducer 135is an ultrasonic transducer, such as but not limited to, piezoelectricultrasonic transducer (PZT). Some embodiments may also include a float.In such an embodiment, the float floats on the surface of the fluidcontained within the tank and is configured to reflect acoustic wavesignals. The level transducer 135 generates an acoustic wave signal,which propagates through the fluid contained within the level focus tube140. The acoustic wave signal propagates toward the surface of thefluid. The acoustic wave signal reflects off of the surface of thefluid, contained within the level focus tube 140, and travels backtoward the level transducer 135.

The temperature sensor 120 senses a temperature of the fluid within thetank. In one embodiment the temperature sensor 120 is a thermocouple. Inanother embodiment, the temperature sensor 120 is a thermistor. In yetanother embodiment, the temperature sensor 120 is a resistancetemperature sensor. In yet another embodiment, the temperature sensor120 is an infrared temperature sensor. The temperature sensor 120outputs the sensed temperature to the control system 300 (FIG. 6). Insome embodiments, the level sensor 115 and the temperature sensor 120are combined into a combination sensor capable of sensing both a leveland a temperature.

The speed-of-sound sensor 125 is configured to sense a speed-of-sound,of the fluid within the tank. A sensed speed-of-sound may be used todetermine a quality of the fluid, for example, a specific gravity of thefluid. The speed-of-sound sensor 125 includes a sensing area 142, aspeed-of-sound transducer 145, and a reflector 150. The speed-of-soundtransducer 145 acts as both a transmitter and receiver. In someembodiments, the speed-of-sound transducer 145 is an ultrasonictransducer, for example, a piezoelectric ultrasonic transducer (PZT). Inoperation, the speed-of-sound transducer 145 generates an acoustic wavesignal, which propagates through the fluid toward the reflector 150. Theacoustic wave signal reflects off of the reflector 150 and travels backtoward the speed-of-sound transducer 145.

The capacitive sensor 130 determines a dielectric constant of the fluidwithin the tank. The capacitive sensor 130 includes a capacitive plate155, a sensing channel 160, and a capacitive substrate 165. Asillustrated in FIG. 1, a portion 167 of the capacitive plate 155 acts asthe reflector 150, and is configured to reflect the acoustic wave signalback toward the speed-of-sound transducer 145. The capacitive plate 155of the capacitive sensor 130 is in contact with, or proximate, thehousing 105. In some embodiments, the capacitive plate 155 is in contactwith a continuous surface, or portion, 169 (FIG. 3) of the housing 105.For example, the continuous portion of the housing 105 is an unbrokenportion of the housing 105 having no through-holes. In some embodiments,the capacitive substrate 165 is a printed-circuit board (PCB).

FIG. 3 illustrates an exploded view of the capacitive plate 155 and thecapacitive substrate 165. As illustrated, the capacitive plate 155includes a first portion 171, a second portion 172, and a third portion173. Additionally, as illustrated, the capacitive substrate 165 includesa first plate 176, a second plate 177, and a third plate 178. In someembodiments, the first plate 176, the second plate 177, and the thirdplate 178 are formed of copper or a similar material. In someembodiments, the first plate 176, the second plate 177, and the thirdplate 178 are etched into the capacitive substrate 165. In someembodiments, the surface area of the second plate 177 approximately fourtimes to approximately five times larger than the surface area of thefirst plate 176.

FIG. 4 illustrates an enlarged view of the capacitive plate 155, sensingchannel 160, and capacitive substrate 165. In some embodiments, thecapacitive plate 155 is formed of copper or a similar material. Thecapacitive plate 155 includes a first surface 170 and a second surface175. The first surface 170 is exposed to the sensing area 142 and isconfigured to contact the fluid contained within the sensing area 142.The second surface 175, of the first and second portions 171, 172, is incontact with, or proximate to, the continuous portion 169 of the housing105, while the second surface 175, of the third portion 173, is exposedto fluid within the sensing channel 160. As illustrated, the capacitiveplate 155 is proximate a first side 180 of the housing 105, while thesubstrate 165 is proximate a second side 182, opposite the first side180, of the housing 105.

The capacitive plate 155, the sensing channel 160, and the capacitivesubstrate 165 form a plurality of capacitors. For example, a firstcapacitor A (FIG. 4) is formed by the first portion 171, of thecapacitive plate 155, and the first plate 176, with the housing 105 (forexample, continuous portion 169 of the housing 105) acting as aninsulator. The second capacitor A′ (FIG. 4) may be formed by the secondportion 172, of the capacitive plate 155, and the second plate 177, withthe housing 105 (for example, continuous portion 169 of the housing 105)acting as an insulator. The third capacitor B may be formed by the thirdportion 173, of the capacitive plate 155, and the third plate 178, withthe housing 105 (for example, continuous portion 169 of the housing 105)and fluid within the sensing channel 160 acting as insulators. Duringoperation, the fluid to be sensed may flow into the sensing channel 160,thus the third capacitor may be formed by the third portion 173, of thecapacitive plate 155, and the third plate 178, with the housing 105 (forexample, continuous portion 169 of the housing 105) and the fluidcontained within sensing channel 160 acting as insulators.

In some embodiments, a seal 185 is configured to prevent fluid fromentering between the first and second portions 171, 172, of thecapacitive plate 155, and the housing 105. In the illustratedembodiment, the seal 185 is located between the second portion 172 andthe first portion 171. In some embodiments, the seal 185 may be formedof a rubber or polymer material. In other embodiments, the seal 185 maybe formed of an epoxy.

In the illustrated embodiment, the capacitive plate 155 further includesa slope, or angled, portion 190. In the example illustrated, the angledportion 190 is configured to reflect any stray speed-of-sound acousticwave signals, such that the stray speed-of-sound acoustic wave signalsdo not interfere with detection of the reflected speed-of-sound acousticwave signals discussed above.

FIG. 5 is a circuit diagram modeling a circuit 200 of the sensing system100 according to some embodiments of the application. As illustrated,circuit 200 models a capacitive sensor power input 205, capacitor A,capacitor A′, capacitor B, capacitor C1, capacitor C2, and a capacitivesensor output 210. As illustrated, in some embodiments, capacitor A′ mayhave an alternating current (AC) behavior similar to that of a shortcircuit. Such behavior may be a result of the surface area of the secondplate 177 (of capacitor A′) being approximately four times toapproximately five times larger than the surface area of the first plate176 (of capacitor A), and the space between the second portion 172 ofthe capacitive plate 155 and the second plate 177 (of capacitor A′)being substantially less than the space between the third portion 173and the third plate 178 (of capacitor B). In some embodiments,capacitive sensor power input 205 and capacitors C1 and C2 are includedin or mounted on the PCB 110. In such an embodiment, PCB 110 iselectrically connected to capacitive PCB 110. In other embodiments, PCB110 and the capacitive substrate 165 are combined into a single PCB.

In the model illustrated, capacitor A is in a series-type configurationwith capacitor C1, while capacitor B is in a series-type configurationwith capacitor C2. Capacitor A and C1 are in a parallel-typeconfiguration with capacitors B and C2 and capacitive sensor AC(alternating current) voltage input 205. Capacitors C1 and C2 havepredetermined capacitance values. In some embodiments, capacitor C1 hasa capacitance value approximately equal to the capacitance value ofcapacitor B, when water is present in the sensing area 142 at a nominaltemperature (for example, approximately 30° C.). In some embodiments,capacitor C2 has a capacitance value approximately equal to thecapacitance value of capacitor A at the nominal temperature. Capacitor Ahas a capacitance value dependent temperature, while capacitor B has acapacitance temperature dependent on temperature and the fluid presentwithin the sensing channel 160.

In operation, a dielectric constant of the fluid within the sensing area142, and thus the sensing channel 160, may be determined based on thecapacitance value of capacitor B. The capacitance value of capacitor Bmay be determined based on: the AC input voltage at capacitive sensorpower input 205; the sensed temperature from temperature sensor 120; thecapacitance value of capacitor A, which in some embodiments isdetermined based on the sensed temperature from temperature sensor 120;the predetermined capacitance values of C1 and C2; and the voltagepresent at capacitive sensor output 210. In some embodiments, thedielectric constant of the fluid within the sensing area 142 may bedetermined using a look up table stored in memory (for example, memory325 (FIG. 6)).

In some embodiments, to calibrate the sensing system 100, an ideal fluidis placed in the sensing channel 160 at a nominal temperature (forexample, 30° C.). The AC input voltage at capacitive sensor power input205 may then be adjusted until the voltage present at capacitive sensoroutput 210 is approximately zero volts AC.

Once calibrated, a fluid to be sensed may then be placed in the sensingchannel 160. The voltage present at capacitive sensor output 210 maythen be monitored, and any deviation (for example, a positive ornegative change in AC voltage) may indicate that the fluid to be sensedis not ideal. A deviation of the voltage present at capacitive sensoroutput 210 caused by a deviation in temperature may be ruled out bymonitoring the sensed temperature from temperature sensor 120. In someembodiments, a look up table may be used to determine that the deviationof the voltage present at capacitive sensor output 210 corresponds tothe sensed deviation in temperature. If the deviation of the voltagepresent at capacitive sensor output 210 is not due to a temperaturechange, an indication, based on the deviation of the voltage present atcapacitive sensor output 210, may then be output to a user. Such anindication may indicate that the fluid is not ideal.

FIG. 6 is a block diagram illustrating a control system 300 of thesensing system 100. In some embodiments, the control system 300 iscontained, partially or completely, on the PCB 110. The control system300 includes a controller 305, a power module 310, an input/output (I/O)module 315. The controller 305 includes a processor 320 and memory 325.The memory 325 stores instructions executable by the processor 320. Insome instances, the controller 305 includes one or more of amicroprocessor, digital signal processor (DSP), field programmable gatearray (FPGA), application specific integrated circuit (ASIC), or thelike.

The power module 310 receives power and outputs a nominal power to thecontrol system 300 and controller 305. In the illustrated embodiment,the power module 310 receives power from an external device (forexample, a control system of a vehicle). In other embodiments, the powermodule 310 may receive power from another power source, such but notlimited to, a battery and/or a renewable power source. The I/O module315 provides wired and/or wireless communication between controller 305and the external device.

The control system 300, via the controller 305, is communicativelycoupled to the temperature sensor 120, the level transducer 135, thespeed-of-sound transducer 145, capacitive sensor power input 205, andcapacitive sensor output 210.

In operation, the controller 305 receives the sensed temperatureinformation from the temperature sensor 120, controls the leveltransducer 135 and the speed-of-sound transducer 145 to generate therespective acoustic wave signals, and receives indication of sensedechoes by the level transducer 135 and the speed-of-sound transducer145. The controller 305 then calculates a level time-of-flight (ToF) anda speed-of-sound ToF. Using the sensed temperature, the level ToF, andthe speed-of-sound ToF, the controller 305 may calculate a level, andthus a quantity, of the fluid as well as a speed-of-sound, and thus aquality, of the fluid. In some embodiments, the speed-of-sound sensor125 may further determine a specific gravity of the fluid using thesensed temperature and the speed-of-sound ToF.

Additionally, in operation, the controller 305, via capacitive sensorpower input 205, outputs an alternating-current (AC) power having apredetermined voltage (for example, approximately 3 VAC to approximately5 VAC) and senses a voltage at capacitive sensor output 210. Thecontroller 305 may calculate a dielectric constant of the fluid based onthe sensed voltage at capacitive sensor output 210.

FIG. 7 is a flow chart illustrating an operation, or process, 400 of thesensing system 100 according to some embodiment. It should be understoodthat the order of the steps disclosed in process 400 could vary.Although illustrated as occurring in parallel order, in otherembodiments, the steps disclosed may be performed in serial order.Furthermore, additional steps may be added (for example, diagnostics) tothe process and not all of the steps may be required. The sensing system100 determines a level of the fluid using the level sensor 115 (block405). The sensing system 100 determines a speed-of-sound of the fluidusing the speed-of-sound sensor 125 (block 410). The sensing system 100determines a relative dielectric constant of the fluid using thecapacitive sensor 130 (block 415). The sensing system 100 outputs thelevel, speed-of-sound, and/or the relative dielectric constant (block420).

FIG. 8 is a flow chart illustrating an operation 500 for sensing a levelof the fluid according to some embodiments. It should be understood thatthe order of the steps disclosed in process 500 could vary. Furthermore,additional steps may be added to the process and not all of the stepsmay be required. Controller 305 controls the level transducer 135 togenerate an acoustic wave signal (block 505). The acoustic wave signaltravels toward a surface of the fluid contained within the focus tube140 (block 510). The acoustic wave signal reflects off of the surfaceand travels back toward the level transducer 135 as one or more echoes(block 515). The controller 305 receives an indication that one or moreechoes have been received by the level transducer 135 (block 520). Thecontroller 305 determines a level ToF based on the received one or moreechoes (block 525). The controller 305 receives a sensed temperature ofthe fluid from the temperature sensor 120 (block 530). The controller305 determines a level of the fluid based on the level ToF, the sensedtemperature, and a speed-of-sound of the fluid (block 535). In someembodiments, the controller 305 further determines a quantity of thefluid based on the level ToF, the sensed temperature, the speed-of-soundof the fluid, and a known dimension of the tank. In some embodiments,the speed-of-sound of the fluid may be determined by the speed-of-soundsensor 125. The controller 305 then outputs the level and/or quantity ofthe fluid (block 540).

FIG. 9 is a flow chart illustrating an operation 600 for sensing aspeed-of-sound of the fluid according to some embodiments. It should beunderstood that the order of the steps disclosed in process 600 couldvary. Furthermore, additional steps may be added to the process and notall of the steps may be required. Controller 305 controls thespeed-of-sound transducer 145 to generate an acoustic wave signal (block605). The acoustic wave signal travels toward portion 167 of thecapacitive plate 155 (block 610). The acoustic wave signal reflects offof portion 167 and travels back toward the speed-of-sound transducer 145as one or more echoes (block 615). The controller 305 receives anindication that one or more echoes have been received by thespeed-of-sound transducer 145 (block 620). The controller 305 determinesa speed-of-sound ToF based on the received one or more echoes (block625). The controller 305 receives a sensed temperature of the fluid fromthe temperature sensor 120 (block 630). The controller 305 determines aspeed-of-sound of the fluid based on the level ToF and the sensedtemperature (block 635). In some embodiments, the controller 305 furtherdetermines a quality of the fluid based on the speed-of-sound ToF andthe sensed temperature. The controller 305 then outputs thespeed-of-sound and/or quality of the fluid (block 640).

FIG. 10 is a flow chart illustrating an operation 700 for sensing adielectric constant of the fluid according to some embodiments. Itshould be understood that the order of the steps disclosed in process700 could vary. Furthermore, additional steps may be added to theprocess and not all of the steps may be required. The controller 305outputs an input voltage (via capacitive sensor power input 205) tocapacitor A, capacitor B, capacitor C1, and capacitor C2 (block 705).The controller 305 senses a voltage present at capacitive sensor output210 (block 710). The controller 305 receives a sensed temperature of thefluid from the temperature sensor 120 (block 715). The controller 305calculates a relative deviation of the voltage present at capacitivesensor output 210 from zero volts AC (block 720). The controller 305determines if the relative deviation is equal to approximately zero(block 725). If the relative deviation is approximately zero, operation700 cycles back to block 705.

If the relative deviation is not equal to approximately zero, thecontroller 305 determines if the relative deviation is due to a changein temperature (block 730). In some embodiments, the controller 305determines if the relative deviation is due to a change in temperatureby using a look up table. If the relative deviation is due to a changein temperature, operation 700 cycles back to block 705. If the relativedeviation is not due to a change in temperature, an indication it outputto the user (block 735). In some embodiments, the indication informs theuser that the fluid is not ideal.

FIG. 11 is a flow chart illustrating an operation 800 for providing asystem configured to sense a relative dielectric constant of the fluid.It should be understood that the order of the steps disclosed in process800 could vary. Furthermore, additional steps may be added to theprocess and not all of the steps may be required. The housing 105including the continuous surface 169 having a first side and a secondside is provided (block 805). The capacitive plate 155 having a firstsurface and a second surface is provided (block 810). As discussedabove, in some embodiments, the first surface is configured to contact afluid to be sensed, while the second surface is proximate the first sideof the continuous surface 169. Substrate 165 is then provided proximatethe second side of the continuous surface 169 (block 815). A capacitancevalue between the capacitive plate 155 and the substrate 165 isdetermined (block 820). A relative dielectric constant of the fluid isdetermined based on the capacitance value (block 825).

Thus, embodiments provide, among other things, a sensor configured todetermine a level and/or quantity, a speed-of-sound and/or quality, anda dielectric constant of a fluid. Various features and advantages ofcertain embodiments are set forth in the following claims.

What is claimed is:
 1. A fluid sensor including a sensing areaconfigured to receive a fluid, the fluid sensor comprising: a transducerconfigured to output an ultrasonic wave through the fluid; and acapacitive sensor including a capacitive plate configured to reflect theultrasonic wave toward the transducer.
 2. The fluid sensor of claim 1,further comprising a controller configured to: determine atime-of-flight of the ultrasonic wave; receive a temperature, from atemperature sensor, of the fluid; and determine a speed-of-sound of thefluid based on the time-of-flight and the temperature.
 3. The fluidsensor of claim 1, wherein the capacitive sensor further includes asensing channel.
 4. The fluid sensor of claim 3, wherein the capacitivesensor further includes a substrate.
 5. The fluid sensor of claim 4,wherein a first capacitor is formed between a first portion of thecapacitive plate and the substrate and a second capacitor is formedbetween a second portion of the capacitive plate and the substrate. 6.The fluid sensor of claim 5, wherein the sensing channel is providedbetween the second portion of the capacitive plate and the substrate. 7.The fluid sensor of claim 5, wherein the first capacitor and the secondcapacitor are electrically connected to a fourth capacitor, a fifthcapacitor, and an alternating-current power source.
 8. The fluid sensorof claim 1, further comprising a controller configure to determine anoutput voltage; determine a relative deviation of the output voltage;and output a signal based on the relative deviation.
 9. A method ofsensing a fluid, the method comprising: outputting, via a transducer, anultrasonic wave through the fluid; and reflecting, via a capacitivesensor having a capacitive plate, the ultrasonic wave.
 10. The method ofclaim 1, further comprising: determining, via a controller, atime-of-flight of the ultrasonic wave; receiving, via the controller, atemperature, from a temperature sensor, of the fluid; and determining,via the controller, a speed-of-sound of the fluid based on thetime-of-flight and the temperature.
 11. The method of claim 1, whereinthe capacitive sensor further includes a sensing channel.
 12. The methodof claim 11, wherein the capacitive sensor further includes a substrate.13. The method of claim 12, further comprising: forming, between a firstportion of the capacitive plate and the substrate, a first capacitivecircuit.
 14. The method of claim 13, further comprising: forming,between a second portion of the capacitive plate and the substrate, asecond capacitive circuit.
 15. The method of claim 14, wherein thesensing channel is provided between the second portion of the capacitiveplate and the substrate.
 16. The method of claim 14, wherein the firstcapacitor and the second capacitor are electrically connected to afourth capacitor, a fifth capacitor, and an alternating-current powersource.
 17. The method of claim 9, further comprising: determining, viaa controller, an output voltage; determining, via the controller, arelative deviation of the output voltage; and outputting a signal basedon the relative deviation.